We intend to study the protein-nucleic acid (and nucleic acid-nucleic acid) interactions which provide the basis for gene expression and its regulation. Our approach is to identify and use nucleotide sequencing methods to analyze the structures of relevant control regions in DNA and RNA molecules. Their mode of interaction with RNA polymerases, ribosomes or their subcomponents, RNA processing enzymes, or DNA recognition proteins involved in genetic translocation will then be examined using both chemical and physical techniques. The role of nucleic acid secondary structure will receive special attention. Three systems, each with particular advantages for exploring certain interactions, have been chosen: 1) The importance of mRNA'rRNA base pairing to the initiation of protein synthesis in prokaryotic and eukaryotic cells will be further defined using RNA bacteriophase and synthetic messengers. The role of E. coli ribosomal protein Sl in facilitating mRNA binding to the ribosome will be investigated. 2) The ribosomal RNA operons of E. coli will be used to study the structures of exceptionally strong promoters for RNA polymerase, the features specifying recognition of a natural substrate by RNase III, and the role of transcribed spacer regions in rRNA biogenesis. Cloning of the rRNA promoters will allow selection of mutants in genes regulating rRNA transcription. Processing of the rRNA transcript from the eukaryote Dictyostelium discoideum will be examined for comparison. 3) Studies of the molecular mechanism of translocation will focus on the transposon gamma delta, present on the F factor of E. coli. Knowledge of DNA sequences within the termini of the element and at its insertion sites, as well as identification of protein(s) encoded by gamma delta, should assist in elucidating the molecular requirements for translocation.